Laser-Induced Breakdown Spectroscopy as a Promising Nanotechnology for Cadmium and Chromium Detection in Aqueous Solutions

Laser-induced breakdown spectroscopy (LIBS) is an atomic emission spectroscopic nanotechnology used for determining sample element compositions. In this study, chemical replacement combined with surface enhanced laser-induced breakdown spectroscopy (CR-SENLIBS) was applied to improve the detection sensitivities of cadmium and chromium in aqueous solutions. By utilizing the chemical replacement effect, Cd2+ and Cr3+ ions from the liquid phase were enriched on the surface of the aluminum alloy forming a solid replacement layer. Technical abbreviations were explained upon their initial use. The unitary and mixed aqueous solutions of 2.5–50 μg/mL CdCl2 and CrCl3 were dropped into aluminum plates and subsequently dried. Afterwards, LIBS experiments were conducted the samples and the aluminum plates. LIBS spectra were collected in the visible optical spectrum region immediately after microplasma generation. LIBS spectra were compared with theoretical LIBS database NIST of American National Institute of Standard and Technology. The calibration curves were constructed. The CR-SENLIBS showed a much better detection sensitivity and accuracy for both unitary and mixed solutions of CdCl2 and CrCl3. The limits of detection (LODs) for cadmium and chromium have been calculated. The LODs for Cd equal 0.127 μg/mL for unitary solution and 0.178 μg/mL for mixed solution. The LODs for Cr equal 0.085 μg/mL for unitary solution and 0.114 μg/mL for mixed solution. Experimental results show that CR-SENLIBS is a perspective method for improving the detection sensitivities of trace cadmium and chromium in aqueous solutions, which provides a way for wider application of LIBS in water quality monitoring.